1. Field of the Invention
This invention relates to a method for the synthesis of antimony pentafluoride (SbF.sub.5) and supported catalyst thereof. More particularly the term "synthesis" is used to include the preparation of SbF.sub.5 from fresh raw materials or to recover the antimony from a spent fluoroantimonate catalyst and in effect remanufacture the catalyst using the recovered antimony.
2. Related Information
Isooctanes or trimethylpentanes (TMP) are among the most desirable components of motor alkylate gasoline and 2,2,4-trimethylpentane (isooctane) has long been the standard of measurement for the anti-knock properties of gasoline.
Motor alkylate isooctane in commercial refineries is prepared by the alkylation of isobutane with butenes in the presence of a strong acid catalyst. Two acids currently used in alkylation plants are concentrated sulfuric acid and hydrofluoric acid. The drawbacks to the use of the sulfuric or hydrofluoric acid processes are readily apparent. Large quantities of the acids, which are highly corrosive, dangerous to handle and potentially a hazard to the environment, are required. Alternative catalysts for these alkaylations are safer particulate solid catalysts such as zeolites (U.S. Pat. Nos. 3,665,813 and 3,706,814); sulfated zirconia (European Patent 0174836); perfluoropolymersulfonic acid (U.S. Pat. Nos. 4,056,578 and 4,180,695) and antimony pentafluoride/acid on a carbon support (U.K. Patent 1,389,237). Other catalyst compositions which have been found to be initially active for alkylation include supported HF-antimony pentafluoride, (U.S. Pat. No. 3,852,371); a Lewis Acid and Group VIII metal intercalated in graphite, (U.S. Pat. No. 3,976,714); and a cation exchange resin complexed with BF.sub.3 and HF, (U.S. Pat. No. 3,879,489). U.S. Pat. No. 4,918,255 describes a process for alkylating isoalkanes with olefins using a Lewis acid such as boron trifluoride, boron trichloride, antimony pentafluoride or aluminum trichloride deposited on inorganic oxide such as a wide pore zeolite, SiO.sub.2 or Al.sub.2 O.sub.3. Japanese Patent Application 85/251672 discloses the production of hexafluoroantimonate salts by the addition of hydrogen peroxide to a reaction mixture of HF and Sb.sub.2 O.sub.3 and reaction with acidic NaF.
Antimony pentafluoride is a desirable catalyst for alkylation because liquid acids are eliminated, however, spent catalyst can require handling and disposal. In addition antimony pentafluoride is expensive and the supply sources limited.
U.S. Pat. No. 5,157,196 discloses a process utilizing a catalyst comprising an acid washed silica treated with antimony pentafluoride and subsequently treated with isoalkane at low temperature used for paraffin alkylation by passing the alkane-catalyst mixture through a plug flow reactor where a minor amount of olefin is introduced to contact the alkane-catalyst mixture and react to form alkylate and the alkane-catalyst-alkylate mixture is passed through the reactor with a minimum of back mixing to restrict the reaction of alkylate with olefin, thus substantially preventing polymerization. Results of up to five barrels of alkylate per pound of catalyst have been reported.
It is a particular feature of the present invention that SbF.sub.5 may be recovered from spent catalyst and used as the source of antimony for the process of preparing SbF.sub.5.